Step one: Decide the brand: Nikon or Canon. Buying a digital SLR is more than just the camera body. You lens, and many many accessories.There are a few articles on photo.net which are really good although a little out of date. For a update see: Canon or Nikon
Step two: decide on Camera: most likely Canon XSi, or Nikon D60, or D80
Step three: accessories: here is an example using Canon you will have an idea how you have to get the essential accessories: click for essential accessories
Step four: where to buy: B&H, amazon or Costco